JP-2010-532448A, JP-2010-73705A, JP-10-18888A, and JP-10-47140A disclose a fuel injection controller which controls a fuel injector. Especially, JP-10-47140A discloses a fuel injection controller having a high speed response. A conventional fuel injection controller supplies comparatively large voltage for opening the fuel injector. While the fuel injector is fully opened, the fuel injection controller supplies comparatively small electric current for maintaining the fuel injector fully opened. Further, the conventional fuel injection controller supplies a reverse direction voltage to perform a demagnetization of the exciting circuit, when the fuel injector will be fully closed.
A fuel injection quantity of a fuel injector is adjusted by controlling a valve opening period of the fuel injector. In order to obtain small injection quantity, it is necessary to shorten the valve opening period of the fuel injector. However, in the small injection quantity, an error of injection quantity is significant. Thus, an accurate injection quantity control is difficult. For example, the error of fuel injection quantity is generated by various factors, such as an error of the mechanical shape of a fuel injector, an error of electric current, and an error of voltage.
In order to obtain small injection quantity, further improvements are necessary in a fuel injection controller.